Equations not needed for this response. Perhaps you have read about or seen (on
ID: 1699948 • Letter: E
Question
Equations not needed for this response.Perhaps you have read about or seen (on a TV program) astronauts practicing "zero g maneuvers" on an airplane being flown in a parabolic arc.
The zero gravity feeling lasts as long as the plane stays in the parabolic arc. It occurs throughout the arc; that is, both on the up and the down legs. However, most pilots chicken out before the arc intersects the earth's surface so the feeling does not last very long. :)
Since the Earth's gravity is still substantial in the atmosphere where such planes fly, explain why the astronauts experience weightlessness under such circumstances. Even though such conditions are far from literally being zero gravity, why is it reasonable to compare such weightlessness to an absence of gravity?
If your car leaves the ground for a few seconds as it goes over a hill you will experience a similar sensation until it lands back on the pavement. Why is this?
Explanation / Answer
My physics professor explained it like this. Space shuttles don't fly straight up because the gravity would pull them back eventually. Instead they fly up at angle. then when they start to fall back down, they have velocity or whatever heading perpendicular to the earth. that way the shuttle falls back down, but it misses. then it goes through the same process continually and it is in orbit. the astronauts experience this because they are constantly falling towards the Earth, but they miss hitting it because they have enough velocity to miss the earth when they get close to it.
it is reasonable because there is no such thing as weightlessness. Weightlessness is the affect of gravity (an acceleration acting on us at all times. On earth it is 9.81 m/s^2 on average). What we call weightlessness is actually freefall. Astronauts are in constant freefall. freefall is when the vector sum of all forces acting on you along the y-axis is equal to the aceleration due to gravity. If you are standing right now, you are not in free fall because the normal force is acting on you in the positive direction making your acceleration in y direction zero.
As far as the car goes, I assume it is the same as the shuttle, except it doesn't miss because it isn't going fast enough. lol. but it does stay in the air for a bit of time.
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